This invention relates generally to apparatus for measuring and testing using optics and in particular to an optical measuring device for measuring angles using plural images.
1. Field of the Invention
In the manufacture and adjustment of precision devices, for instance in the adjustment of the magnetic heads of magnetic disk storage devices, two or more axes frequently have to be aligned with respect to each other. The alignment could be where the axes must be in parallel, vertically spaced, or at an angle relative to each other. The particular problem in the adjustment of the magnetic heads of magnetic disk storage devices, especially with the very high storage density of present day devices, is that the admissable deviation from parallelism between the read/write gap of the magnetic head and of the radius line of the magnetic disk are so small that conventional angle measuring devices are not capable of sensing the deviations.
2. Prior Art
At present, the alignment is generally performed by means of a microscope having a reticle. The magnetic gap, or an edge of the magnetic head previously made parallel to the magnetic gap, is aligned to the reticle by an operator looking through the microscope. The angle of deviation d.theta. is a function of the lateral deviation dy of the edge to be adjusted. The angle of deviation varies according to the equation:
DY=1/2 .times. LENGTH OF EDGE X ARC D.theta.
It is therefore obvious that the edge lengths to be placed within the image field of a high magnification microscope only permits angular adjustments of relatively low precision.
If, for example, an edge has a length of 350 microns and is to be aligned to within .+-.0.5 degrees in parallel, the lateral displacements of the edge has to be detected within a precision of less than 1.5 microns. Although the measuring precision can be increased to a certain extent by a strong magnification, only part of the edge will be physically in the image field. The reticle must be repeatedly displaced along the length of the edge that is to be adjusted. This increases the measuring precision and permits adjustment within relatively close limits but the length of time involved to perform this test makes that check prohibitive.
It is, therefore, an object of the present invention to provide a method for measuring extremely small angles with a high precision without time consuming adjustments.
Complex optical systems using optical wedges has been used to measure the angular orientation of one body relative to another about an axis of rotation. Split images were produced in transposition of spaced-apart portions of a target reticle of the first body. The target reticle is optically split by the optical wedges or mirrors operating as a means of splitting the image of the target reticle into two halves. The complex optics used the optical deviation of the axis technique to accomplish the transposed halves of the target reticle.
It is, therefore, another object of the present invention to provide an apparatus for measuring the deviation angle of one body relative to another by using simple optical devices.